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Public Health Impact of Including Two Influenza B Strains in Seasonal Influenza Vaccines Carrie Reed Martin Meltzer Lyn Finelli Anthony Fiore Vaccines and Related Biological Products Committee February 18, 2009 The findings and conclusions in this presentation are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention (CDC)

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Influenza B viruses Circulate globally every year Subdivided into two lineages; currently co- circulate annually –B/Yamagata –B/Victoria On average, fewer severe complications and deaths than A (H3N2) viruses –Severe complications and deaths caused by influenza B do occur in all age groups –Children appear to have higher rates of infection

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Influenza B virus lineage and trivalent influenza vaccine Protection after vaccination with one lineage against other lineage is limited Co-circulation of both lineages over the past several years means some degree of mismatch between vaccine and circulating strain inevitable

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Question If switch to quadrivalent vaccine (QIV): Compared to trivalent vaccine (TIV), what would be the incremental reduction in cases, hospitalizations, and deaths?

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Modeling the public health impact Include last 10 influenza seasons –Characteristic natural variability from season to season Population average, all ages –May not capture variability by age group Spreadsheet-based model –User can change inputs –e.g., age-specific data; update to future influenza seasons

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Step 1: Vaccine Production For a given production output: Fewer doses of QIV produced than TIV Question: Over past 10 seasons, how many doses of QIV could have been produced? Question: How does this relate to the number of doses administered that year?

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Step 1: What does the model do? Optimizes the number of doses of a QIV that could be produced with the same production capacity as TIV Compares the number of QIV doses available to the TIV doses administered

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Data needed Annual doses of TIV vaccine produced Percent reduction in growth of B strain compared to each A strain –Varies by season Annual doses of TIV administered

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Sample page of spreadsheet model with data INPUT: Doses trivalent produced INPUT: Reduced production from A to B viruses

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Conclusions, Part 1 When TIV vaccine supply was similar to demand (e.g., 2002-2005) –Fewer doses of QIV potentially produced than doses of vaccine administered When TIV supply greatly exceeds demand (e.g., 2005-2008) –Reduced QIV doses available would still exceed the number of vaccines administered

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Step 2: Public Health Impact If switch to QIV vaccine: –Over the past 10 influenza seasons; –What would have been the incremental reduction in cases, hospitalizations and deaths?

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Step 2: What does the model do? Calculates burden of influenza during each season –Outcomes: rates of illness, hospitalization, death Compares rates expected with a QIV to rates observed with TIV –Simple model, population average –Can be further refined as data allows

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EXAMPLE 3: 2004-2005 Virologic surveillance: 25% of circulating strains were influenza B viruses; 26% not the lineage in vaccine Problems with production led to decreased supply and administration of vaccine Loss in coverage if fewer doses of QIV available (15% fewer persons vaccinated) Net increase of 151,566 cases with QIV

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Sensitivity analysis: Variability by season and potential reduced coverage

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Conclusions, Part 2 When TIV supply was similar to demand (e.g., 2002-2005) –Fewer persons vaccinated with QIV, could have led to modest increases in morbidity or mortality When TIV supply greatly exceeds demand (e.g., 2005-2008) –Vaccine-induced protection against both B lineages using QIV could have led to modest reduction in morbidity and mortality

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Limitations Assumptions from limited data and to simplify model –Data entered as a population average, but may vary by: Age Health impact (cases, hospitalizations, deaths) Strain / lineage –Spreadsheet model can be adapted in future as data is available Past may not accurately predict the future –Unknown with what frequency different B lineages will circulate –User can change any inputs in the model and recalculate an estimated impact

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Public Health Impact of Including Two Influenza B Strains in Seasonal Influenza Vaccines Policy Considerations Anthony Fiore Vaccines and Related Biological Products Committee February 18, 2009 The findings and conclusions in this presentation are those of the author and do not necessarily represent the views of the Centers for Disease Control and Prevention (CDC)